Microstructural and mechanical behavior of SnCu-Ge solder alloy subjected to high temperature storage

This paper addresses the effect of high temperature storage on the microstructural and mechanical behavior of novel SnCu-Ge solder alloys. Eutectic Sn99.3Cu0.7 solder was micro-alloyed with the addition of minor Ge as an anti-oxidant and to improve the wetting performance of the alloy. The addition of Ge significantly reduced the aging degradation of the alloy. The ultimate tensile strength and yield stress dropped within first few days of aging and the fracture strain increased with aging. The corresponding microstructure changed after annealing at 125 degrees C for 3 months; the average grain size of the beta-tin portions of the microstructure increased with aging and the imbedded IMC particles segregated along and/or within the grains. Based on growth kinetics and activation energy arguments, we suggest that the addition of Ge restricts the Cu diffusion into the alloy and inhibits the IMC growth.